This invention relates to a fluoroolefin base multicomponent copolymer which is soluble in various organic solvents, curable at relatively low temperatures and useful as a paint vehicle.
Fluororesins are generally excellent in weather resistance, heat resistance and chemical resistance. Accordingly paints using a fluororesin as the vehicle have been developed for application to chemical plants, buildings and other constructions, machinery and food containers. Recently much attention has been directed to solvent-thinned paints using a fluororesin which is soluble in organic solvents and curable at normal temperature. Fluororesin paints of this type are comparable to solvent-thinned paints using other conventional resins in the ease of application and provide paint films superior in chemical resistance and weather resistance.
To render a fluororesin soluble in practicable organic solvents, usually it is necessary to reduce crystallinity of the fluroresin by copolymerization to thereby accomplish internal plasticization. Furthermore, there are some other problems to be resolved in using a soluble fluororesin as a paint vehicle. The problems include how to retain a desirable degree of rigidity or shear modulus in the modified fluororesin, how to control the molecular weight of the fluororesin with a view to desirably adjusting the viscosities of paints and how to select and control the kind and amount of functional groups to be introduced into the fluororesin in order to render the resin curable. The cost of production also has to be taken into consideration. It is not easy to reach a balanced solution for all the problems.
U.S. Pat. No. 4,631,326 shows a copolymer of, essentially, chlorotrifluoroethylene, a fatty acid vinyl ester and a hydroxyl-containing allyl ether. This copolymer is soluble in various organic solvents and curable with a polyisocyanate or a melamine resin. The cured copolymer is hardly soluble in organic solvents in which the uncured copolymer is soluble. Therefore, a solution of this copolymer is useful as a liquid vehicle of a paint.
As the vinyl ester in a copolymer of U.S. Pat. No. 4,631,326 it is favorable to use the ester of a fatty acid having not more than 3 carbon atoms in the alkyl group, and in particular either vinyl acetate or vinyl propionate, for physical properties of the copolymer in the form of a coating film and also for the cost of production. However, the copolymer is very low in solubilities in aromatic solvents low in polarity such as toluene and xylene, though the same copolymer exhibits high solubilities in organic polar solvents. It is rather unfavorable to use a polar solvent in a paint, because when the paint is recoated on a paint film or used for repairing a damaged paint film or directly coated on a plastic surface the polarity of the solvent is liable to cause swelling, cracking or clouding or the overlaid paint film or the substrate surface. In the recent automobile industry, for example, it is prevailing to use an aromatic solvent low in polarity represented by xylene as the solvent for paints.